Dermatoglyphic fluctuating asymmetry in twins and singletons ... been reported to influence development of traits such as birth weight and I.Q.. no significant .... the Student Newman Keuls multiple range test for unequal samples with a = 0.05.
Hereditus 110: 211-215 (1989)
Dermatoglyphic fluctuating asymmetry in twins and singletons THERESE ANN MARKOW’ and IRVING I. GOTTESMAN’ ’Department of Zoology, Arizona State University, Tempe, U.S.A . , and ’Departments of Psychology and Pediatrics, University of Virginia, Charlottesville, U .S . A .
MARKOW,T.A. and GOTTESMAN, 1.1. 1989. Dermatoglyphic fluctuating asymmetry in twins and singletons.
- Heredims 110: 21 1-215. Lund. Sweden. ISSN 0018-0661. Received November 24. 1988. Accepted January 9, 1989
The influence of twinning on developmental stability was measured by comparing fluctuating asymmetry in dermatologlyphic traits in monozygotic twins, dizygotic twins, and singletons. Despite reports that twinning has been reported to influence development of traits such as birth weight and I.Q.. no significant difference in fluctuating asymmetry was found between different zygotic categories.
Therese Ann Markow, Department of Zoology, Arizona State University, Tempe, Arizona 85287-1501, U.S.A.
Estimating heritability by the use of twins requires assumption of a certain degree of comparability between twin and singleton populations. This is not always warranted. Certain peculiarities of twins invalidate this assumption. Twinship per se has been considered a type of “birth defect” by some (BULMER 1958). Double occupancy of the human uterus appears to repress development, as evidenced by such phenomena as reduced birth weight and intelligence among twins (HUSEN1959, 1960, 1963; MYRIANTHOPOULOS et al. 1972). These effects raise the question of the degree of stress associated with uterine sharing and the degree to which development is ultimately affected by that stress. One means of assessing the degree of developmental stress employs measures of asymmetry in bilateral traits. In a bilaterally symmetrical organism, both sides of the body develop as mirror images of each other. Exceptions to this include those directional asymmetries which are typical of a given species, such as number of lobes in the right and left human lung. Another type of asymmetry, fluctuating asymmetry, occurs when the developmental plan is not expressed in the same way in both sides of a bilaterally symmetrical organism. Such interference with the developmental plan, or developmental instability, may result from various environmental influences which the organism is not able to buffer during its development (WADDINGTON 1957).
In humans, a variety of bilateral quantitative traits have been examined for evidence of developmental instability. Some bilateral traits are more suitable than others for studies of fluctuating asymmetry. Ideally, a trait should not only be quantifiable, but it should not be subject to environmental alterations after birth. Traits in the dentition, such as cusp number or tooth diameter have been studied for fluctuating asymmetry but their usefulness may be limited by problems such as dental decay or normal wear. Dermatoglyphic traits have been useful in various etiological studies in addition to providing diagnostic tools for zygosity determination (HOLT1968; SCHAUMANN and ALTER1976). Several dermatoglyphic features, because they are easily quantified, have been utilized in studies of fluctuating asymmetry associated with various disorders (ADAMS and NISWANDER 1967; WOOLF and GIANAS 1976,1977; MARKOW and WANDLER 1986). In many cases twin research is conducted with the assumption that findings may be extended to singletons. We directly test this assumption for developmental buffering abilities. In the present study, we ask if twinning is associated with developmental instability by comparing fluctuating asymmetry levels for two related dermatoglyphic traits, Total Finger Ridge Count, and Absolute Finger Ridge Count, among monozygotic twins, dizygotic twins, and singletons.
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T. A. MARKOW AND I. I. GOTTESMAN
Hereditus 110 (IYXY)
Methods Subjects Twins. -The twin sample used in the present study was originally selected in Minnesota for an investigation of the heritability of personality reported by GOTTESMAN (1963). Zygosity was determined by the following blood group systems (RACEand SANCER 1968): ABO, MNSs, R h , P, Lutheran (Lu), Kell (K), Duffy (Fy), Kidd (Jk), and Lewis (Le). These 1 procedures are discussed in detail in GOTESMAN (1963). Thirty-four pairs of twins were diagnosed as dizygotic (DZ) and an equal number as monozygotic (MZ). Singjeton subjects. - The 30 male and 30 female adult singleton prints were obtained from the files of John D . Douthit (Certified Fingerprint Consultant and Identification Officer with the Minnesota Bureau of Criminal Apprehension) and represented the same population as the adolescent Minnesota twins. All had been applicants for jobs in Minnesota requiring a "clear" criminal justice system record such as the insurance, banking, and brokerage industries. N o other information is available about them. Fig. 1. A diagram of some basic dermatoglyphiccharacters. Finger 1 shows an ulnar loop; finger 2, a radial loop; finger 3, a whorl; finger 4, a tented arch; and a plain arch is on Dermatoglyphics finger 5. Palmar triradii a thru d are seen at the bases of Finger Printing. - Mr. D. Douthit, using the Faurot fingers 2 through 5 . inkless method, fingerprinted about half of the twins and, after being tutored in the technique, one of the authors (IIG) fingerprinted the rest. Analysis ofprints. -Ridge counts were recorded by the procedures described in HoLr (1968). In this method the ridges crossing or touching a straight line running from the triradius to the core of the pattern are counted. Neither the triradius nor the final ridge in the center of the pattern were included in the count. The three basic fingerprint patterns are shown in Fig. 1. When performing ridge counts, arches receive a score of zero. Loops yield ridge counts to only one triradius, but whorls and related patterns have two triradii and therefore two counts. Studies of Total Finger Ridge Count (TFRC) employ only the larger of the two counts on each whorl while Absolute Finger Ridge Count (AFRC) includes both values. The former is a measure of a single trait, pattern size, while A F R C reflects pattern intensity, a trait with two components, pattern size and type of pattern (HOLT 1968). Differences between the two ridge count traits will usually only occur when whorls arc present. The range of values from AFRC is greater than for TFRC, a feature which is important in certain investigations. In the
present study both T F R C and A F R C are reported upon. Of the twins identified and described by GOTESMAN (1963), we were able to utilize the finger prints of 12 pair of monozygotic males, 17 pair (plus one twin) of monozygotic female twins, 10 pair of dizygotic male twins, and 19 pair of dizygotic female twins.
Statistical unalysis offinger print data TFRC and AFRC and their right minus left differences were examined by treating the counts on each finger (1-5) as separate traits. The descriptive statistics and analyses of variance procedures were carried out on the Arizona State University IBM mainframe computer using SAS software. Ridge counts and R-L values were compared between sexes and zygosity categories. In order to detect true fluctuating asymmetry (FA), which is defined as random size deviation between bilaterally paired characters, the existence of directional asymmetry ( D A ) in which the enlarged side is consistently the same, or antisymmetry (AS) in which one side is consistently enlarged but the exact side is random, was evaluated.
Herediras / I 0 (IYXYJ
DERMATOGLYPHICFLUCTUATINGASYMMETRY
2 13
Results
(1968) for the distribution for total ridge counts (F 1-5). Total finger ridge counts, by finger, for males and Before approaching the question as to whether females of each group, are shown in Table 1. Signi- twinning increases developmental instability deficant differences in counts are observed among tectable as fluctuating asymmetry (FA differences), groups for fingers 1,4, and 5 on the right hand and 1 the data were first evaluated for the presence of and 4 on the left. For the most part these differences sizekale effects, directional asymmetry, and antiappear to be related to sex, with females having symmetry. The presence of any relationship lower ridge counts. Twins do not have lower between the size of the character (ridge count) and TFRCs. the degree of R-L difference was sought by plotting Values for AFRC are shown in Table 2. Fingers ridge counts against R-L differences (PALMER and 1 and 5 of the right hand show significant differences STROBECK 1986). between groups as do fingers 4 and 5 of the left, In the absence of any relationship between asymalthough these differences are not always reflected metry and character size, the remaining analyses by the subset groups generated by the multiple were performed on untransformed data. Antisymrange tests. As with TFRC, no reduction or metry is suggested if R-L distributions show signiincrease in AFRC is associated with twinning. ficant platykurtosis. In no case were distributions The Kolmogorov Smirnov test for goodness of fit platykurtic. The biggest potential problem in de(SIEGEL1956) revealed that, for all fingers, the tecting for R-L differences is the presence of direcdistributions of TFRC and AFRC deviated signi- tional asymmetry (DA). We tested for directional ficantly from normality. Ridge counts on fingers 1 asymmetry with analysis of variance using hand as a and 4 tend to be higher than for other fingers. These factor. Significant D A was found for finger 1 in findings are similar to those reported by HOLT both TFRC and AFRC ( F = 11.9, df 1, 11, 338, p
Table 1 . Total finger ridge counts in different zygosity groups by finger and sex Fingers on right hand Group
1
SIF 15.2k1.3” SIM 20.6k1.Ih MZF 16.6k1.1’ MZM 21.1k1.0b DZF 14.9+1.2” DZM 21.0k0.7h F P
6.83
